Method for vapor condensation and recovery

ABSTRACT

Methods for recovery of precursor vapor from a gas and precursor vapor mixture used in a deposition process. The gas and precursor vapor mixture is passed through a multitude of heat transfer surfaces in a heat conducting housing causing the precursor vapor to condense. The precursor vapor in liquid form is then collected after condensation.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a divisional application of U.S. patentapplication Ser. No. 13/680,331, filed Nov. 19, 2012, which is based onand claims the benefit of U.S. provisional patent application Ser. No.61/641,519, filed May 2, 2012, the contents of which are herebyincorporated by reference in their entirety.

BACKGROUND OF THE DISCLOSURE

Thin film deposition for semiconductor device fabrication is generallycarried out through a gas phase process, such as chemical vapordeposition (CVD), plasma-enhanced chemical vapor deposition (PECVD) oratomic layer deposition (ALD). In such a process a liquid chemicalprecursor is generally vaporized with the help of a carrier gas to forma vapor/gas mixture. The mixture then flows into a deposition chamberfor thin film deposition on a substrate. The deposition chamber isusually maintained at a vacuum in order to meet the desired processconditions.

Following deposition, the gas/vapor mixture then flows through a vacuumpump for exhaust to the ambient atmosphere. During its passage throughthe pump, the vapor, which is chemically reactive, can react with thepump oil to change the physical and/or chemical characteristics of theoil. Over time, the pump oil becomes contaminated with the reactiveprecursor vapor and is no longer capable of maintaining the depositionchamber at the desired vacuum pressure. When this occurs, the systemmust be shut down for pump maintenance, leading to the loss ofproductivity for the deposition system.

To reduce the frequency of pump maintenance, various exhaust treatmentdevices have been developed and used in the semiconductor industry. Theyrange from devices that use high temperature plasma to decompose theprecursor vapor to systems that inject vapor to react with the precursorvapor to render them less harmful. While these measures can prolong orextend the operating life of the pump, they do not provide a permanentsolution for the problem.

SUMMARY OF THE DISCLOSURE

In this disclosure, an apparatus is described for recovery of precursorvapor from a gas and precursor vapor mixture that is used for depositionin a semiconductor fabrication process. The apparatus comprises ahousing with an inlet for the gas and precursor vapor mixture to flowinto the housing. The housing also includes a first outlet for the gasof the gas precursor vapor mixture to flow out of. A second outlet ofthe housing permits the precursor liquid formed from the precursor vaporcondensation to be discharged from the housing. The housing ismaintained at a temperature sufficient for the precursor vapor tocondense and form the precursor liquid.

The apparatus may include a thermal electric cooler for controlling thetemperature of the housing to a selected value for condensing theprecursor vapor to form the precursor liquid. The housing may be made ofa heat conducting metal such as aluminum. A multitude of heat conductingsurfaces for heat transfer are included in the housing which dissipatesheat outside of the housing.

This disclosure also includes a method for recovery of precursor vaporfrom a gas and precursor mixture after use in deposition in asemiconductor fabrication process. After use in deposition, thegas/precursor mixture is directed through a multitude of heat transfersurfaces in a heat conducting housing causing precursor vapor in the gasand precursor mixture to condense. The precursor liquid formed throughcondensation from the precursor vapor is collected in a reservoir.

The method may include the additional steps of removing heat produced byprecursor vapor condensation through the use of a thermal electriccooler so that the heat is removed through a multitude of heat transfersurfaces to outside of the housing.

Additionally, the gas and precursor mixture may be passed through afilter to remove suspended particles in the mixture prior to the gas andprecursor mixture's use in deposition.

This disclosure also includes a method of fabricating integrated circuitdevices including the steps of generating a gas and precursor vapormixture; passing the gas and precursor vapor mixture through adeposition chamber to form a thin film on a substrate; and condensingunused precursor vapor of the gas and precursor vapor mixture in acondenser to collect condensed precursor vapor in liquid form.

This method also may include the additional step of removing heatproduced by the precursor vapor condensation through the use of athermal electric cooler that dissipates the heat through a multitude ofheat transfer surfaces to outside of the housing.

Additionally, the gas and precursor mixture is passed through a filterto remove suspended particles in the mixture prior to the gas andprecursor mixture entry into the deposition chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a semiconductor thin film depositionsystem in which the vapor recovery condenser of the present disclosureis used to condense vapor for recovery.

FIG. 2 is a vertical sectional view of the vapor condensing apparatus ofthe present disclosure in its preferred embodiment.

FIG. 3 is a horizontal sectional view of the vapor condensing apparatusof the present disclosure in its preferred embodiment.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The present disclosure describes a method and an apparatus forcondensing the precursor vapor to form a precursor liquid downstream ofthe deposition chamber. The condensed liquid is substantially unchangedin its physical and/or chemical characteristics from the originalprecursor liquid used for film deposition. The collected liquid can bepurified for recycling and reused or be disposed of in a safe manner tominimize the potential harmful effect on the environment.

FIG. 1 is a schematic diagram of a semiconductor thin film depositionsystem including a vapor recovery condenser of the present disclosureplaced downstream of the deposition chamber to reduce pump oilcontamination and improve the reliability of the film deposition system.Like reference characters will be used for like elements throughout thefigures. The system includes a vapor generating apparatus 30, which canbe a bubbler or a direct liquid injection vaporizer. The more widelyused direct liquid injection vaporizer is shown for convenience.

Vaporizer 30 of FIG. 1 is provided with a gas inlet, 32, a liquid inlet,34, and an outlet 36. Gas inlet 32 is connected to a pressurized gassource, 10, containing the desired carrier gas. Liquid inlet 34 isconnected to a pressurized liquid source 20 containing the precursorliquid to be vaporized. Vaporizer 30 is generally heated to a specificoperating temperature. As the gas and liquid flow through the vaporizerat the desired rates of gas and liquid flow, the gas is heated and theliquid is vaporized to form vapor at substantially the same temperature.The resulting gas/vapor mixture then flows out of vaporizer 30 throughoutlet 36 into a filter, 80, to remove suspended particles that may bepresent in the gas/vapor mixture. The clean gas/vapor mixture then flowsinto deposition chamber 40 through chamber inlet 42 to form thin film onsubstrate 50. The gas/vapor mixture then flows out of deposition chamber40 through outlet 44.

The system is typically provided with gas and liquid flow controllers inorder to control the gas and liquid flow rates to the desired set pointvalues. The vaporizer and deposition chamber are usually heated byelectric heaters. They are also provided with temperature controllers inorder to operate the vaporizer and the deposition chamber to theirrespective temperature settings. In addition, the deposition istypically carried out in vacuum. The required vacuum pressure istypically achieved by means of a vacuum pressure sensor and a vacuumpressure controller in order to operate the system at a specific vacuumpressure. For simplicity, all of these controllers including the sensorsthat form part of the control system for the semiconductor thin filmdeposition tool are not shown explicitly.

A variety of carrier gases has been used for thin film deposition. Inertgases such as nitrogen, helium and argon are quite common. Gases such ashydrogen and oxygen are also used in some applications. Precursorliquids such as TEOS (tetra ethyl ortho silicate), TiCl₄ (titanium tetrachloride), various metal organic compounds, and compounds such as TEMAH(tetraethyl amino hafnium) and TEMAZ (tetraethyl amino zirconium) forhi-k (high dielectric constant) film deposition by ALD (atomic layerdeposition) processes are also widely used.

In the conventional vapor generation and deposition system a vacuumpump, 70, is located downstream of deposition chamber 40 in order tomaintain the deposition chamber 40 to a desired vacuum pressure. Vacuumpump, 70, then exhausts the gas/vapor mixture to the ambient atmosphere.100211 The thin film deposition system of FIG. 1 also includes a vaporcondensing apparatus 60, which is provided with an inlet 62 for thevapor and carrier gas mixture from deposition chamber to enter, anoutlet 66 for the condensed liquid to exit, an external reservoir 80 forcapture and store the condensed liquid, and an outlet, 64, for thecarrier gas to exit. The carrier gas is substantially free of theprecursor vapor, which has been condensed and collected by the vaporcondensing apparatus 60, then enters pump 60 for exhaust to the ambient.

Unlike prior art exhaust treatment systems that are designed to destroythe precursor vapor to prevent or reduce pump contamination, the vaporcondensing apparatus of the present disclosure condenses the precursorvapor without substantially changing its chemical nature or its physicalcharacteristics. The condensed precursor liquid is generally quite pure.The collected liquid can be stored in the external reservoir 80.Alternatively, the condensed liquid can be stored internally in thevapor condensing apparatus 60 from which the stored liquid can bedrained out of the system from time to time for safe disposal or reuse.

FIG. 2 shows a vertical sectional view of vapor condensing apparatus 60of FIG. 1. The apparatus is shown generally located at 100 with aninlet, 62, for the gas/vapor mixture to enter and an outlet 66 for thecondensed liquid to flow out. The gas, which is substantially free ofthe precursor vapor, then exits the vapor condensing apparatus 100through outlet 64 and flows into vacuum pump 70 for exhaust to theambient atmosphere.

The vapor condensing apparatus 100 generally operates under vacuum. Itis provided with a vacuum tight envelop 105 with removable cover plates,110 and 115, that are held in place by screws, 106, and gaskets, 108.Alternatively, cover plates 110 and 115 can be permanently welded inplace to form a vacuum tight envelop. Apparatus 100 is generallyconstructed of a heat conducting metal, such as aluminum. Athermoelectric cooler 120 is placed in good thermal contact with theheat conducting metal envelop 105 in order to control its temperature toa suitably low value, typically below about 25 degrees C. Within thevacuum tight envelop, there are multitudes of heat transfer surfaces 160and 170 that are in good thermal contact with the heat conductingenvelop. Since heat transfer surfaces 160 and 170 are in good thermalcontact with the heat conducting metal envelop 105, the temperature ofthese heat transfer surfaces 160 and 170 is also substantially the sameas that of envelop 105 and is thus also below about 25° C.

As the gas/vapor mixture flows along heat transfer surfaces 160 and 170within the vacuum tight envelop 105, precursor vapor will condense onthese heat transfer surfaces to cause it to form liquid on the surfaces.This precursor condensed liquid will then flow by gravity along thesesurfaces into the annular liquid collecting trough 180 below. Thecondensed liquid will then flow out of trough 180 through exit 66 intoexternal reservoir 80 shown in FIG. 1

When vapor condenses on the heat transfer surfaces 160 and 170, thevapor condensation release heat. This heat will be transferred byconduction to the vacuum tight envelop 105 for it to be carried away bythe thermoelectric cooler 150 and rejected to the ambient atmosphere bythe external heat transfer surface 130. A cooling fan 140 will draw airfrom ambient causing it to flow in the indicated direction of the arrows150 and blowing this air back to the ambient in the direction of arrows190.

Thermoelectric cooler 120 is typically operated by DC power andcontrolled by a temperature sensor to a selected temperature by feedbackelectronic control. Such controls are familiar to those skilled in theart of temperature control the thermoelectric cooler and will not befurther described.

FIG. 3 is a horizontal sectional view of the vapor condensing apparatusof the present disclosure in its preferred embodiment. The internal heattransfer surfaces are spaced apart from each other by gaps of emptyspaces 180. These empty spaces form flow channels through which thevapor/gas mixture can flow through, thus permitting the vapor tocondense on the vertical surfaces 160 and 170. Similarly, external heattransfer surfaces 130 also form vertical flow channels 135 to allowcooling air from the ambient atmosphere to flow through and be blown bycooling fan 140 in the general direction of arrows 190.

Although the present invention has been described with reference toreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

What is claimed is:
 1. A method for recovery of precursor vapor from agas and precursor mixture after use in deposition in a semiconductorfabrication process, the method comprising: directing said gas andprecursor mixture after deposition to pass through a multitude of heattransfer surfaces in a heat conducting housing causing precursor vaporin said gas and precursor mixture to condense; and collecting precursorliquid formed from the precursor vapor condensation in a reservoir. 2.The method of claim 1 including the additional steps of removing heatproduced by precursor vapor condensation by a thermal electric cooler;and dissipating the heat so removed through a multitude of heat transfersurfaces outside said housing.
 3. The method of claim 1 including theadditional step of passing said gas and precursor mixture through afilter to remove suspended particles in the mixture prior to the gas andprecursor mixture's use in deposition.
 4. A method of fabricatingintegrated circuit devices including the steps of: generating a gas andprecursor vapor mixture; passing said gas and precursor vapor mixturethrough a deposition chamber to form a thin film on a substrate; andcondensing precursor vapor of said gas and precursor vapor mixture in acondenser to collect condensed precursor vapor in liquid form.
 5. Themethod of claim 4 including the additional steps of removing heatproduced by precursor vapor condensation by a thermal electric cooler;and dissipating the heat so removed through a multitude of heat transfersurfaces outside said housing.
 6. The method of claim 4 including theadditional step of passing said gas and precursor mixture through afilter to remove suspended particles in the mixture prior to the gas andprecursor mixture entry into said deposition chamber.